Respiratory: anatomy and physiology


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Presentation to participants undertaking the: Critical Care Transition Program at ACT Health, 2008

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  • The conducting airways consist of the nasal passages, mouth, pharynx, larynx, trachea, bronchi, and bronchioles.
    Conducting Zones: the first 16 generations of branching make up the conducting airways, and the last 7 constitute the respiratory zone (or respiratory and transitional zone). BR, bronchus; BL, bronchiole; TBL, terminal bronchiole; RBL, respiratory bronchiole; AD, alveolar duct; AS, alveolar sacs.
    AS have a volume of ~2500ml in adults (70m2 – the size of a tennis court)
    Pores of Kohn – allow for collateral ventilation (interconnecting AS) – few in children,
  • Therefore, when there is no movement of air into or out of the lungs, alveolar and atmospheric pressures have reached an equilibrium.
  • Lung Volumes:
    Tidal Volume: volume of air inhaled and exhaled with each breath
    Inspiratory Reserve Volume: Maximum volume of air that can be inhaled after a normal breath
    Expiratory Reserve Volume: Maximum volume of air that can be exhaled after a normal breath
    Residual Volume: Volume of air remaining in the lungs after maximum exhalation
    Lung Capacities:
    Vital Capacity: Maximum volume of air exhaled from the point of maximum inspiration
    Inspiratory Capacity: Maximum volume of air inhaled after normal expiration
    Functional Residual Capacity: Volume of air remaining in the lungs after normal expiration
    Total Lung Capacity: Volume of air in the lungs after a maximum inspiration and equal to the sum of all four volumes.
  • What is needed to make it accurate?: Need normal peripheral perfusion (Hb, flow and adequate O2%).
  • CO2 stimulates respiratory centre to increase rate and depth of breathing
    Lungs – exhalation of CO2 rapid response, occurs within minutes, reaches max within hours.
  • L-R
    PCO2 20,40,80
    Temp: 30,37,43
    Increased O2 affinity = shift to the Left = O2 given up less readily (less 02 available to tissues)
    Decreased O2 affinity = shift to the right = O2 given up more readily (more 02 available to tissues)
  • L-R
    PCO2 20,40,80
    Temp: 30,37,43
    Increased O2 affinity = shift to the Left = O2 given up less readily (less 02 available to tissues)
    Decreased O2 affinity = shift to the right = O2 given up more readily (more 02 available to tissues)
  • Carbon dioxide Narcosis Normal respiratory drive is adjusted by PaC02 levels.
    A reduction in the ph of CSF provides a stimulus to breath.Individuals with chronically elevated PaCo2 (eg. COAD) have reduced sensitivity to this mechanism. They are dependant on a low Pao2 levels to provide a respiratory drive.
    During mechanical ventilation,administration of high Fio2 can potentiate hypoventilation in that you take away the respiratory drive.
    Oxygen Toxicity
    High Fio2 administration (100% > 24hrs).The body metabolizes oxygen,the end product of this process are oxygen free radicals which are then neutralized and excreted. Cell damage and death – lung tissue, eye (newborns), etc…
    Nerve –
    Main nerve supply through 2 phrenic nerves (each half of the diaphram has 1)
    Bronchial muscle is innervated by both the parasympathetic (vagus) and sympathetic.
    Central chemoreceptor:
    Inspiratory area: major stimulus is Co2 concentration – transmits input from the peripheral chemoreceptor. Below conscious thought.
    Expiratory area: located in a separate area of the medulla not active unless there is some distress. How the interaction occurs between the inspiratory and expiratory areas is not known.
    Pneumotaxic area: located in the pons, participates continuously in the inspiratory effort – limits TV of air inspired.
    Apnrudyic area: to cause excessive inflation of the lungs with occasional expiratory effort.
    Peripheral chemoreceptor's
    Decreased O2 levels in the arterial blood are censored by the carotid body and aortic arch – transmitted to respiratory centre – increased phrenic nerve impulse.
    Also sensitive to Co2 – but less then central receptors which act first!
  • Acidosis exposes the myocardium to impulse & contractile dysfunction. The myocardium is sensitive to low cellular pH
  • Elasticity: is the return of the original shape of matter after the alteration by an outside force
    Compliance: is how easily a tissue is stretched, and therefore inflation of the lungs
    Resistance: is determined by the radius of the airway, therefore an decrease is diameter of the airway will result in an increase in resistance and therefore the amount of effort required to ventilate the patient will be increased.
    Pressure: the total volume of gases exert pressure against the walls of the alveoli (such as O2, NO, CO2 and other gases)
    Gravity: gravity effects ventilation depending on the position of patient, position of insult or injury
  • Respiratory: anatomy and physiology

    2. 2. • Describe airway structures • Describe the mechanics of breathing • Identify chemical receptor / nerve impulses of breathing • Understand the mechanisms of gas exchange Objectives
    3. 3. • Respiratory Structures • Respiratory Zones • Respiratory Pressures • Respiratory Volumes and Capacity • Ventilation and Perfusion • Gas Exchange • Respiratory Regulation • Mechanics of Ventilation Overview
    4. 4. Anatomy and Physiology Respiratory Structures
    5. 5. Anatomy and Physiology Respiratory Zones
    6. 6. Anatomy and Physiology Partitioning of Respiratory Pressures
    7. 7. Anatomy and Physiology Boyles Law Increase V = Decreased P Decreased V = Increased P
    8. 8. Anatomy and Physiology Boyles Law • Air flows from a region of higher pressure to a region of lower pressure. • To initiate a breath, airflow into the lungs must be precipitated by a drop in alveolar pressures.
    9. 9. Anatomy and Physiology Respiratory Volumes and Capacity
    10. 10. Anatomy and Physiology perfusion without ventilation = shunt normal ventilation and perfusion ventilation without perfusion = dead spaceairway venous blood arterial blood Ventilation and Perfusion
    11. 11. Gas Exchange • Oxygen is carried in the blood. 2% dissolved in plasma, 98% combined with Hb. • Hb Cells have no capacity to store O2. What does an SpO2 reading tell us? What is needed to make it accurate?
    12. 12. Gas Exchange H+ + HCO3  H2CO3  CO2 + H2O • Atmosphere  Alveoli  Blood  Tissues / Cells • Diffuses from areas of higher to lower concentration • Oxygen tension at sea level 75-100mmHg • Oxygen delivery to tissues is dependent on the ease with which Hb gives up its oxygen once its reached the tissues
    13. 13. Gas Exchange
    14. 14. Gas Exchange
    15. 15. Gas Exchange
    16. 16. Gas Exchange PaO2 drops and PaCO2 increases Muscles work to meet O2 demand Muscles tire and become less efficient Acidosis Acidosis impairs muscle activity
    17. 17. • Elasticity • Compliance • Resistance • Pressure • Gravity Mechanics of Ventilation